Abstract: The low-resistance motion characteristics of subaqueous debris flow is an important topic to study the mechanism of subaqueous debris flow. The water pressure at the bottom of the subaqueous debris flow is an important factor to reduce the resistance. Rotating flume tests are performed to reproduce the low-resistance motion of subaqueous debris flow and to measure the reach angle of dense granular flow granular flow in the subaqueous debris flow. The newly developed measurement system is used to measure the water pressure at the bottom of the dense granular flow granular flow, and to evaluate the static and additional water pressure at the bottom of the dense granular flow granular flow. The experimental results and theoretical analysis show that the additional water pressure at the bottom of the subaqueous debris flow is related to the low resistance motion of the subaqueous debris flow. The maximum thickness of the dense granular flow granular flow is 12 mm, while the maximum additional water pressure is 69 Pa. This research provides an experimental method for revealing the mechanism of low resistance motion of subaqueous debris flow. The newly developed measurement system provides a new way for the water pressure measurement of debris flow with low resistance motion.